Heretofore fluid systems have been employed for controlling the rate of movement of hydraulic motors and, in particular, systems which have a single rod piston that has equal pressure responsive areas. An example of such a cylinder and system for operating the cylinder is disclosed in my U.S. Pat. No. 4,738,101 issued Apr. 19, 1988. There are a variety of applications when it is desirable to have a piston with only one piston rod.
A common requirement in many hydraulic systems is that the piston of a reciprocatory fluid motor is driven at a relatively high speed up to a certain point in its forward stroke, and then is driven through the remainder of its forward stroke at a relatively low speed under a relatively high applied pressure. A known system for accomplishing this result employs a proportional directional control valve and unequal displacement single rod ended cylinder.
The single rod three chamber cylinder referred to above in my patent includes two chambers to which equal area piston surfaces are exposed at the rod end side and the head end side of the piston. A third chamber hydraulically isolated from the first two chambers is exposed to a third area on the piston which faces the head end side of the piston. This particular type of cylinder is well adapted to a rapid traverse, low speed feed application in that rapid traverse in either direction is possible by utilizing the first two chambers, and the pressure applied during the feed portion of the forward stroke may be augmented by supplying fluid under pressure to act against the third area. There is no known method of using a proportional directional control valve in a feed system to drive a three chambered cylinder as described above.